This invention relates to a tuning control for a radio frequency device such as a transmitter, receiver or transceiver, and particularly to a single knob tuning arrangement for providing both fine and coarse tuning. The rate at which the tuning knob is rotated determines the resolution or the rate at which the frequency is changed with respect to the amount of dial rotation.
Radio communications equipment of modern design used various means for controlling frequency. One common technique is to use crystals or frequency synthesizers to provide for coarse frequency determination, and to provide an operator controlled dial or knob for fine tuning. The knob may control a permeability tuned oscillator (PTO) or a frequency synthesizer.
In one modern receiver, the PTO is designed to cover a 500 kHz range of frequencies (from 5.05 to 5.55 mHz, for example). The rate at which this dial controls frequency is determined by the components within the PTO, and typically may vary in the range of from 15 to 30 kHz per dial revolution.
In another modern radio communications device, the dial is connected to an optically encoded disc, and pulses generated by phototransistors as the markings on the disc pass thereby are applied to the input of a counter which determines the frequency of the device. Switch means may be used to determine the resolution of the tuning dial, e.g., with the switch in one position, the dial resolution may be 10 Hz per revolution; in another position, 100 Hz per revolution; and in still another position, 1 kHz or 10 kHz, etc. In the above devices, the dial resolution must be switch selected by the operator.
In another tuning system, the speed at which the dial rotates control dial resolution. For example, in U.S. Pat. No. 3,835,384, the resolution may be 10 Hz, 100 Hz, or 1 kHz, all automatically selected according to the rate at which the dial is rotated. In this prior art device, as the speed of dial is increased, there will be a sudden change in dial resolution, making it difficult for the operator to control accurately the output frequency.